Too Deep or Not Too Deep?: A Propensity-Matched Comparison of the Analgesic Effects of a Superficial Versus Deep Serratus Fascial Plane Block for Ambulatory Breast Cancer Surgery

Background and Objectives Serratus fascial plane block can reduce pain following breast surgery, but the question of whether to inject the local anesthetic superficial or deep to the serratus muscle has not been answered. This cohort study compares the analgesic benefits of superficial versus deep serratus plane blocks in ambulatory breast cancer surgery patients at Women's College Hospital between February 2014 and December 2016. We tested the joint hypothesis that deep serratus block is noninferior to superficial serratus block for postoperative in-hospital (pre-discharge) opioid consumption and pain severity. Methods One hundred sixty-six patients were propensity matched among 2 groups (83/group): superficial and deep serratus blocks. The cohort was used to evaluate the effect of blocks on postoperative oral morphine equivalent consumption and area under the curve for rest pain scores. We considered deep serratus block to be noninferior to superficial serratus block if it were noninferior for both outcomes, within 15 mg morphine and 4 cm·h units margins. Other outcomes included intraoperative fentanyl requirements, time to first analgesic request, recovery room stay, and incidence of postoperative nausea and vomiting. Results Deep serratus block was associated with postoperative morphine consumption and pain scores area under the curve that were noninferior to those of the superficial serratus block. Intraoperative fentanyl requirements, time to first analgesic request, recovery room stay, and postoperative nausea and vomiting were not different between blocks. Conclusions The postoperative in-hospital analgesia associated with deep serratus block is as effective (within an acceptable margin) as superficial serratus block following ambulatory breast cancer surgery. These new findings are important to inform both current clinical practices and future prospective studies. Accepted for publication November 27, 2017. Address correspondence to: Faraj W. Abdallah, MD, The Ottawa Hospital General Campus, 501 Smyth Rd, Ottawa, Ontario, Canada K1H 8L6 (e-mail: FAbdallah@toh.ca). This work was supported by departmental funding. F.W.A. and R.B. are supported by the Merit Award Program, Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada. R.B. also receives research support from the Evelyn Bateman Cara Operations Endowed Chair in Ambulatory Anesthesia and Women's Health, Women's College Hospital, Toronto. The authors declare no conflict of interest. Copyright © 2018 by American Society of Regional Anesthesia and Pain Medicine.

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